Slot structure for radio communications system

ABSTRACT

In one embodiment, the present invention includes a slot in a repeating time division frame with a first training sequence, an information sequence after the first training sequence, and a second training sequence after the information sequence. In some embodiments either the first or the second training sequences indicates a type for the information sequence, such as a random access channel message and a traffic channel message, a configuration message, a channel assignment message, or a data traffic message.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of priorcommonly-owned applications, Radio Communications System With a SharedBroadcast Channel, Ser. No. 09/675,274, filed Sep. 29, 2000; Closing aCommunications Stream Between Terminals of a Communications System, Ser.No. 09/813,194, filed Mar. 20, 2001 now U.S. Pat. No. 6,996,060; SpatialProcessing and Timing Estimation Using a Training Sequence in a RadioCommunications System, Ser. No. 09/841,456, filed Apr. 24, 2001 now U.S.Pat. No. 6,650,714 the priorities of which are hereby claimed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention applies to a slot structure in a repeating frameused in time division communications between base stations and userterminals and, in particular, to a slot structure that allows differenttypes of messages to be transmitted interchangeably in the same slot.

2. Description of the Prior Art

Time division mobile radio communications systems such as cellular dataand voice radio systems typically use a repeating frame that includesslots allocated for specific purposes. In a frequency division TDMA(Time Division Multiple Access) system, the repeating frame may includea set of downlink slots. A set of uplink slots is in another frame on adifferent frequency. Broadcast, random access and control channelmessages may each be assigned to specific frequencies that use adifferent frame structure. Within each frame, the slots for each type ofmessage can be optimized for the type of messages that it carriesenhancing efficiency. In a TDD (time division duplex) system, uplink anddownlink slots are in the same frame. In some instances, specific slotswithin the frame may carry some control messages. However, the controland access channels are normally in specifically optimized slots inseparate frames.

Separate broadcast, control and access channel slots allow greatflexibility in designing a wireless radio network of base stations andremote user terminals. However, each channel that is set aside forbroadcast, control or access purposes cannot be used for traffic. Whenthe number of channels is limited in comparison to the demand fortraffic, it is preferred to maximize the traffic usage of all of thesystem's radio capacity.

BRIEF SUMMARY OF THE INVENTION

In one embodiment, the present invention includes a slot in a repeatingtime division frame with a first training sequence, an informationsequence after the first training sequence, and a second trainingsequence after the information sequence. In some embodiments either thefirst or the second training sequences indicates a type for theinformation sequence, such as a random access channel message and atraffic channel message, a configuration message, a channel assignmentmessage, or a data traffic message.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings in which likereference numerals refer to similar elements and in which:

FIG. 1 is a diagram illustrating an example of a standard uplink slotstructure according to one embodiment of the present invention;

FIG. 2 is a diagram illustrating an example of a standard downlink slotstructure according to one embodiment of the present invention;

FIG. 3 is a diagram illustrating an example of a repeating framestructure according to one embodiment of the present invention;

FIG. 4 is a simplified block diagram of a base station on which anembodiment of the invention can be implemented; and;

FIG. 5 is a block diagram of a remote terminal on which an embodiment ofthe invention can be implemented.

DETAILED DESCRIPTION OF THE INVENTION

Overview

In one embodiment of the invention, a unique slot structure for TDD(Time Division Duplex) communications allows different types of messagesto be transmitted in the same slot depending on system needs. The uplinkand downlink slots can both be used for a variety of different types ofmessages including BCH, CCH, RACH, and TCH. The particular message typecan be distinguished by analyzing the date carried in the informationsymbols or from the training sequence. The slot structure also enhancesthe accuracy of timing by placing all of the information symbols betweentwo training sequences. One of the training sequences can be used totransmit control information by selecting it from among a small group ofknown sequences.

In one embodiment, it is contemplated the invention is implemented in aTDD high bandwidth wireless data and voice system, such as ArrayComm'si-BURST™ system. However, it should be appreciated the invention is notlimited to the i-BURST system or any other particular air interface, andin fact, it should become apparent from the description herein that theinvention may find use with a variety of air interface protocols andcommunications systems.

Broadcast Channel (BCH)

The system of the present invention is initiated for each user terminalor remote terminal from the broadcast channel BCH which is transmittedas a burst from the base station to all potential user terminals. TheBCH burst, unlike the traffic channel bursts, is transmitted in alldirections where user terminals may be, typically omnidirectionally butthe specific beam pattern will depend on the network. Accordingly, theBCH burst will create more interference on the system than spatiallydirected or lower power traffic channels TCH. For this reason, the dataand modulation properties of the BCH channel are selected to minimizeinterference.

An example of a broadcast burst structure is shown in Table 1. Some ofthe important BCH burst properties are as follows. The BCH iscomputationally easy to find by scanning in real time having noknowledge of time-slot boundaries. It communicates enough basicinformation to enable a subsequent exchange of configuration request CRand configuration message CM between the base station and the userterminal. The BCH also provides good frequency offset and timing updateinformation to all user terminals, even when the BCH is not specificallydirected toward any one user terminal in particular.

Table 1 summarizes the content of an example of a BCH burst.

TABLE 1 Duration Contents  10 μsec ramp - up 272 μsec frequencycorrection training symbols f₁, f₂, . . ., f₁₃₆ 256 μsec timingcorrection training symbols t₁, t₂, . . . t₁₂₈  16 μsec broadcastpreamble r₁, r₂, . . . r₈ 512 μsec information symbols h′₁, h′₂, . . .h′₂₅₆  10 μsec ramp - down  14 μsec inter-burst guard time

The frequency and timing correction training symbols can be setaccording to any one of many approaches well-known in the art. They canalso be combined, exchanged with a synchronization sequence oreliminated.

The broadcast information symbols are constructed from a 15-bitbroadcast message which is modulated and coded into a 256 bit sequence.The number of symbols as well as the structure and sequence oftransmitted bits can be varied to suit a wide variety of applications.The presently described embodiment has been selected in order tominimize the amount of information transmitted in the BCH as well as tominimize the bit rate. The broadcast channel information symbols providethe information needed for a user terminal to request a configurationmessage from the base station. They also provide information to guideuser terminal handover decisions.

Each broadcast message is mapped into a broadcast burst with theinformation shown in Table 2.

TABLE 2 Broadcast Message Field # of Bits BStxPwr 5 BSCC 7 BSload 3Total 15

BStxPwr is the effective isotropic radiated power of the broadcastmessage. This number indicates the power transmitted by the base stationtaking into account the number of amplifiers and diversity antennasavailable at the base station. For a 10 antenna broadcast channel, basestation power=(2·BStxPwr+10) dBm.

BSCC is the base station color code, used by the user terminal to selecttraining data for uplink bursts and to distinguish broadcasts ofdifferent base stations. In one embodiment, there are up to 128different possible color codes. The color codes can be used to indicatea base station in a different location or a differentmodulator/demodulator set in the same location.

BSload is the load on the base station, used by the user terminal todetermine how frequently to send random access messages. BSload is anindication of the amount of unused capacity the base station has. It canbe different from the number of active registered subscribers becausesubscribers can require different amounts of traffic capacity. BSloadrepresents the transmit and receive bit rates of each modem of the basestation over a period of a few minutes measured against maximum possibleloading.

In one embodiment, the BCH channel is shared by all base stations in thewireless communication system. Using the 7 bit BSCC, up to 128 basestations can be accommodated. The BCH is a time division duplex channelwith a repeating frame. The channel is a single RF carrier frequencyused for uplink and downlink. For high noise environments or forincreased robustness, the BCH can hop frequencies according to apredetermined scheme or be repeated on several different frequencies.The repeating frame includes the downlink BCH for each base station,labeled BS1 etc. as shown in Table 3. The next frame includes the uplinkConfiguration Request CR, labeled CR1 etc. and downlink ConfigurationMessage CM, labeled CM1 etc.

Each frame also includes a number of reserved slots, shown as emptyboxes below. These slots can be used for data traffic, if the broadcastchannel is also used for traffic, for other control messages or reservedto reduce interference on other channels in the network. The frames arerepeated for each respective base station 1 to 128 to build a superframeas discussed in more detail below. After the last CM, CM128, thesuperframe repeats and begins again with the next superframe and the BCHfor base station 1.

TABLE 3 Uplink Downlink Superframe 1 Frame 1 BS1 Frame 2 CR1 CM1 Frame 3BS2 Frame 4 CR2 CM2 . . . . . . . . . Frame 255 BS128 Frame 256 CR128CM128 Superframe 2 Frame 1 BS1 Frame 2 CR1 CM1 . . . . . . . . .

A base station can be considered a collection of base station modemsserving a group of contiguous RF carriers. Alternatively, a base stationcan be an installation with a set of modems at a single site. For othersystem configurations each modem modulator/demodulator set 52, 62 can beconsidered a base station. Each base station is assigned a unique 32-bitbase station identifier, BSID. The BSID is used to derive a base stationcolor code as follows: BSCC=BSID mod 128. As a function of the BSCC, abase station frequency hops, broadcasts BCH, listens for uplink CR, andsends downlink CM. Within a geographical region where radiotransmissions overlap, the BSID should be assigned so that the BSCC isuniquely assigned. No base station should be able to routinely see userterminals that are communicating with a base station of the same colorcode. Likewise, no user terminal should be able to see two base stationsthat are assigned the same BSCC. The total number of base stations aswell as the number of frames in a superframe, the number of slots in aframe and the particular slots used for transmitting BCH bursts, CRs andCMs can be modified to suit particular applications.

To minimize, the data rate of BCH bursts still further, the BSCC andBSload can be removed from the BCH burst. The BCH burst then containsonly training or synchronization and BStxPwr, the only informationdirectly related to handover decisions. The user terminal can stilldistinguish and compare different base stations for selection andhandover decisions based on timing of the received BCH bursts. The userterminal can also direct its CR message to a specific base station asshown in Table 3 based on timing. For a single base station system, theBStxPwr bits can also be deleted. If there is only one base station, itis not necessary to evaluate path loss but only whether the signal canbe received. The rest of the network information can be learned uponregistration, described below. Alternatively, since the BCH includes theBSCC, the user terminal can be programmed to read the BSCC and assumethat BCH bursts with a common BSCC are from the same base station. Inthis way, the user terminal can learn a shortened frame repetitioninterval, and reduce the time needed to register with the system.

Registration

A user terminal forms a relationship with a base station called aregistration. This registration begins by listening to the broadcastchannel and ends with a handover, timeout, or disconnection. The firststep of registration is accomplished by a remote by sending theConfiguration Request burst CR and receiving a Configuration Messageburst CM. The CM contains basic configuration parameters such as hoppingsequence calculation parameters. Using the information from the CM, theuser terminal then opens an unauthenticated stream using a random accessregistration request RA-rreq. This unauthenticated stream carries onlyin-band signaling data used to complete registration and assignment of aregistration identifier RID and paging identifier PID. Using the RIDassigned at the end of the registration stream, the user terminal canopen subsequent streams and it can end registrations. The user terminalcan also open subsequent streams in which it can send packets which areused to perform “network login” to an Internet Service Provider (ISP).

During the registration stream, identities and capabilities areexchanged, operating parameters are set, and a RID and PID are assigned.Later, a new network session may be created and attached to this RID, oran existing session may be handed over. This handover may be fromanother base station, another base station modem on the same basestation (load shifting), or even from a hibernating session on the samebase station modem. The specific details of registration are providedhere as examples only. Many other registration scenarios are alsopossible within the scope of the present invention.

The frame timing is established by the base stations that are in thearea and transmitting on a pre-programmed RF carrier. The carrier may bea frequency hopping or spread spectrum carrier. However, it is preferredthat the carrier be easy to find and be pre-programmed into the userterminals. The base stations, or base station if there is only one,employ GPS or some other precise common timing reference to establishthe frame timing. GPS timing offers the advantage that it is accuratelysynchronized and inexpensively available to all base stations. Thisallows the BCH to be shared by all the base stations with only a minimalguard time in the BCH between base stations.

The base stations then build the BCH frame described above and broadcastin their respective assigned slots. When a user terminal turns on, itscans this well-known, optionally pre-programmed, RF carrier to findbasic frame timing and synchronization. The user terminal scans thiscarrier for BCH bursts, building an RSSI (Received Signal StrengthIndicator) map. From this BCH RSSI map and other factors, the userterminal selects the strongest or the best base station. It also usesthe BCH to precisely adjust its oscillator frequency and adjust itsframe timing reference. This is done using the synchronization andtiming sequences in the BCH burst, described above. Then, using its useror remote terminal ID (UTID) it builds and sends a Configuration RequestCR, timed relative to the BCH burst for that strongest or best basestation. In one embodiment, the CR is scrambled using the BSCC that wasreceived in the BCH from the selected base station.

If the intended base station successfully receives the CR and hasavailable capacity, it unscrambles the CR, and determines the spatialsignature of the user terminal. The user terminal receives aConfiguration Message burst CM in reply. The CM, described in greaterdetail below, contains sufficient information for the user terminal tolearn its distance and RF path-loss to the base station, correct itstiming advance, adjust its power control, and learn the parameters offrequency hopping (e.g. frame numbering and BSCC). Several base stationsmay be probed with a CR to find the closest or the best base station.Based on this information from the CM, the user terminal, when it hasdata to transmit, can start a session, beginning with a random accessregistration request RA-rreq. If resources are available, the basestation sends an Access Assignment AA to the user terminal assigning atraffic channel. The base station and user terminal exchange variousaccess control parameters including encryption keys on this establishedstream. Finally a RID and PID are assigned. Using this RID, the userterminal can establish secure streams (e.g. RA-rts/AA-cts) in which ittransmits and receives internet packets.

The traffic channel includes a data acknowledgement DA or a data invalidDI response to each transmitted data packet. The DA and DI messages aretransmitted as a part of the next data packet from the recipient in thenext slot. In a time division duplex frame, the base station and theuser terminal alternate slots as shown in Table 4. Accordingly, if anyslots are not received properly, the data can quickly be retransmitted.This reduces the size of the data buffers at the respective base stationand user terminal modems. As shown in Tables 3 and 4, uplink slotsalways precede downlink slots and there is a guard time between the twoin order to allow for any synchronization errors or unanticipatedpropagation delays. In one embodiment, each side transmits data packetsin three slots, each slot including ramp-up and ramp-down periods aswell as synchronization bits as is well-known in the art.

TABLE 4 1 2 3 1 2 3 1 2 3 . . . Uplink Slots Guard Downlink Slots GuardUplink Slots Time Time

Periodically, the user terminal scans the BCH to update its RSSI andBSCC map. When it detects a better base station, it may send a CR tothis new base station and possibly handover its network session. Ifsuccessful stream initiation fails too many times, the user terminalenters a timeout state. From timeout, it may try to regain a RID viaRA-rreq, refresh its timing advance using a CR, find a new base stationto which it might handover by scanning the BCH, or even begin fromscratch to re-acquire basic frame timing. If this re-establishment issuccessful, the user terminal may be able to continue its networksession by completing a network session handover to the new basestation.

Channel Considerations

In one embodiment, the network is designed to take maximal advantage ofspatial division multiple access technologies and particularly smartantenna array signal processing. To help maintain reliable spatialchannels in an extremely dense frequency reuse pattern, the network usestime division duplex TDMA where uplink and downlink transmissions arealways on the same frequency. In addition, because many user terminalsare single antenna and transmit and receive omnidirectionally, exceptfor the BCH, an uplink burst is always received before a downlink burstneeds to be sent. This allows downlink bursts to be more accuratelyspatially directed. An uplink training sequence is embedded in everyuplink burst to allow for moderately fast frequency hopping despite anydecorrelation of the spatial channel with frequency.

The frequency hopping sequence may be any one of many differentsequences well-known in the art. The parameters of the frequency hoppingscheme are initially unknown to the user terminal. This maximizes theflexibility of the network and increases the flexibility of the userterminal. As explained below, the frequency hopping parameters aretransmitted to the user in the CM burst.

The robustness of the frequency hopping scheme and the trafficcapabilities of the system are improved if more frequency carriers canbe allocated to the frequency hopping scheme. The BCH carrier isincluded as part of the frequency hopping scheme and, accordingly, usedas a traffic channel. Since any one base station transmits a BCH burstonly once per frame and since traffic is spatially directed to aparticular user, a base station can transmit traffic channel data burstsduring another base station's BCH burst without significantly addinginterference to user terminals that are listening for BCH bursts onneighboring channels. Normally, the user terminal to which the trafficdata burst is directed will not be listening for BCH bursts because itis already in a traffic session.

Because in the present embodiment there are 128 base stations eachassigned to a different slot of the BCH, it is unlikely that the128^(th) portion of the BCH that is assigned to any one particular basestation will overlap with a particular channel in the frequency hoppingtraffic channel scheme while that channel is being used for traffic.However, if it does, the base station broadcasts its BCH burst at itsassigned time, listens for CR messages at its assigned time andtransmits CM bursts in its assigned slot. This ensures furtherconsistent operation of the network. For a user terminal, however, theuse of the BCH carrier as a BCH will interrupt its traffic channelsession. As a result, instead of receiving a data packet burst from thebase station, it will receive the BCH burst.

Even if the user terminal does not recognize this burst as BCH, it willimmediately recognize it as having an invalid format for the expecteddata packet. Accordingly, in the next uplink frame, it will send a datainvalid DI message with its burst and the base station will send theearlier expected data packet in the next available frame in the trafficchannel. In the present timing scheme, the same slot in the next framewill coincide with a Configuration Message slot for that base station.The same slot in the next frame will coincide with a different basestation's assigned BCH slot. However, even if the second slot alsooverlaps with the base station's BCH assignment, the same protocol canapply again. The remote terminal will again send a DI message and afterthe assigned BCH slot has passed, the base station will send theexpected data burst. By relying on the acknowledgment protocol, the datacapacity of the network can be increased to include most of the BCHwithout increasing the complexity of the signaling or processingresources.

The amount of data capacity increase will depend on how much of the RFresources are dedicated to the BCH and how many base stations are in thesystem. If there are a small number of base stations in the system, sothat the BCH frame has a very short repeat, the network can beconfigured so that every BCH slot is used for BCH, greatly reducing theamount of time for a remote user to acquire timing and synchronizationand transmit a configuration request.

Alternatively, the BCH can be configured so that only a small number ofthe possible 128 slots are used for BCH bursts and the rest of thechannel capacity is left open for traffic. If there are a large number(i.e. close to 128) of base stations in the network, then it is unlikelythat a user terminal will be able to receive BCH bursts from more thanten percent of the possible base stations. As a result, the remainingninety percent of the carrier can be used for data traffic withoutaffecting new user terminals scanning for BCH bursts. The base stationcan be programmed with the BSID or BSCC of the nearby base stations sothat it also will not transmit traffic during the BCH slots assigned tothose base stations. The same DI, retransmit scheme described above willcompensate for any conflicts between neighboring BCH slots and thetraffic channel.

Configuration Request CR

CR bursts are distinguished from random access RA and traffic TCHbursts, in part, by a special CR spatial training sequence. The CRtraining sequence is longer than normal and has periodic properties thatmake finding timing alignment especially computationally efficient. TheCR burst is shorter than a standard uplink data burst to allow fortime-delay with unknown distance between the user terminal and basestation. The CR burst is shortened by 86 μsec allowing an uncompensatedtime delay equivalent to a user terminal being about 15 km away from thebase station.

The CR burst is transmitted from a user terminal at an unknown distancefrom the base station. Because of time-of-flight considerations, theuser terminal time base is delayed relative to the base station.Furthermore, its CR transmission is also delayed because its timingadvance is not yet initialized. Shortening the CR burst by 35 μsecallows it to arrive up to 35 μsec late without spilling over into thenext time-slot. These 35 μsec mean that a user terminal 5300 meters fromthe base station can send a CR burst that will land completely withinits time-slot. If this burst is seen by the base station, and repliedto, the corresponding CM will contain a timing advance adjustment whichwill properly position subsequent data bursts.

Table 5 summarizes the content of the example CR burst. The 82information symbols are constructed from the configuration requestmessage using modulation and coding.

TABLE 5 Duration Contents  10 μsec ramp-up 260 μsec training symbols a₁,a₂, . . ., a₁₃₀ 164 μsec information symbols h₁, h₂, . . ., h₈₂  10 μsecramp-down  86 μsec extra guard time  15 μsec inter-burst guard time

CR spatial training is the same for all base stations and the basestation does not necessarily know the location of the user terminalbefore receiving the CR. CRs are transmitted by user terminals at afixed offset from BCH transmissions as shown in Table 3. The resultingtime-multiplexed registration channel easily distinguishes CRs sent todifferent ones of several nearby base stations. Furthermore, CR and CMare scrambled by a function of BSCC ensuring that even if there is someinterference from CRs sent to nearby base stations, the demodulationcapture effect of the BSCC works out any collisions. In one embodiment,the scrambling is performed by taking the encoded bit sequence andexclusive OR'ing it with the output of a linear feedback shift register.Finally the smart antenna spatial resolution ability of the base stationis applied to resolve any remaining ambiguities in received CRs.

A configuration request message is mapped onto a configuration requestburst CR by the physical layer. A configuration message is mapped onto astandard downlink burst by the physical layer. The information symbolsof the present CR burst are mapped out as shown in Table 6. Any of theitems listed below can be deleted and transmitted later during theregistration cycle or not at all based on the needs of the system.

TABLE 6 Configuration Request Message Field # of Bits identity 8 utClass4 txPwr 5 Total 17

-   -   identity is a set of unique random bits for each user terminal        that differentiate simultaneous messages from multiple user        terminals. Because of the randomness and large number of bits,        it is unlikely that two user terminals will select the same        identity code at the same time.    -   utClass identifies user terminal capabilities (highest        modulation class, frequency hopping capabilities, etc. ) This        sequence identifies the type of user terminal that sent the CR.        A palmtop digital assistant might have different capabilities        than a desktop computer with a fixed dedicated antenna. With        utClass, the different capabilities can be distinguished.    -   txPwr represents the power used by the user terminal to transmit        the Configuration Request burst. For example, user terminal        power=(2txPwr−30) dBm.

CR is sent on the control carrier, as an example, exactly 2265 μsecafter receipt of a downlink BCH burst. In this way, an otherwiseuninitialized user terminal can send CR without any knowledge of thefrequency hopping sequence parameters. The CR burst is shorter than astandard uplink time-slot to allow for unknown time-of-flight from theuser terminal to the base station and typically arrives late in theuplink time-slot receive window.

Configuration Message CM

Table 7 summarizes the content of an example Configuration Messageburst. The 494 information symbols are constructed from theconfiguration message using modulation and coding.

TABLE 7 Duration Contents  10 μsec ramp-up  68 μsec training symbols a₁,a₂, . . ., a₁₃₀ 988 μsec information symbols h₁, h₂, . . ., h₄₉₄  10μsec ramp-down  15 μsec inter-burst guard time

The configuration message CM burst is sent on the BCH carrier, exactly 5msec after sending a downlink BCH burst, whenever CR was received on thecorresponding uplink time-slot. Using this timing, CM is directed to therequesting user terminal. CM is also sent in a spatially directed signalbased on the analysis of the spatial signaure, for example parameters,such as DOA and TOA of the uplink CR. Since CM is sent on the BCHcarrier, a fixed time offset from BCH, an otherwise uninitialized userterminal can receive CM without any knowledge of the frequency hoppingsequence parameters.

CM, in response to CR, includes, among other things; the AFN (AbsoluteFrame Number), a larger timing-advance adjustment dynamic range, coarserpower control, and various access control parameters. Table 8,summarizes the content of the CM burst. Any of the items listed belowcan be deleted and transmitted later during the registration cycle ornot at all based on the needs of the system.

TABLE 8 Configuration Message Field # of Bits identity 8 pwrCtrl 4timingAdjust 7 AFN 10 carrierMask 16 racarrierMask 16 raslotMask 3 raDec3 hopping 1 Total 70

The meanings of the symbol sets are as follows:

-   -   identity: the random identity sent by the user terminal in the        CR    -   pwrCtrl: power offset that the user terminal should apply to        future parameter request bursts and random access bursts:        offset=(2·pwrCtrl−16) dB.    -   timingAdjust: timing advance that the user terminal should apply        to future random access bursts: timing advance=timingAdjust μs.    -   AFN: the 10 least significant bits of the Absolute Frame Number    -   carrierMask: bitmap of carriers containing traffic channels    -   racarrierMask: bitmap of carriers containing random access        channels (least significant bit is carrier 0)    -   raslotMask: bitmap of slots containing random access channels        (least significant bit is slot 1). Random access channels occur        where both racarrierMask and raslotMask are nonzero.    -   raDec: AFNs available for random access channels. hopping: if        equal to 1, the relationship between physical and logical        carriers hops each frame.

Random Access-request to Send Burst

As can be seen from the discussion above, after registration, the userterminal has a RID and a PID and a fair amount of information about thenetwork, including all of the data listed in Table 5. This informationincludes an assigned random access channel or set of assigned randomaccess channels and an initial transmit power level. This information isused in generating and sending the RA-rts.

After the user terminal has been registered with a particular basestation, it can open a stream for a data exchange. The opening of astream can be initiated by either the base station or the user terminal.Typically a stream will be opened if either the base station or the userterminal has data to send to the other. This data is buffered until apreset amount has accumulated in a transmit buffer or until a presetamount of time has elapsed. The preset amount can be any non-zero value.If the base station has accumulated transmit data in its buffer for theuser terminal, then it will send a page, described in more detail below,to the user terminal. If the user terminal receives a page or if it hasaccumulated a sufficient amount of data in its transmit buffer, then itwill send, for example, an RA-rts message. This message, as explainedbelow, is a request that a stream be opened to allow the exchange ofdata. The base station upon receiving the RA message will analyze itssystem resource availability and if a suitable channel is available,then it will respond with, for example an AA-cts message. This message,as explained below, identifies a channel and assigns it for the stream.

With the RA/AA exchange, the stream is assigned and all the necessaryinformation for the terminals to communicate has been exchanged. Withthe next uplink slot, the remote terminal will begin sending its dataover the assigned channel. If the stream was initiated by a page fromthe base station, then the remote terminal may not have any data to sendin which case it will send idle bits. The idle bits help the basestation to maintain its spatial parameters for the user when there is nodata received. The base station will use these spatial parameters tosend its data packets or idle bits. In this way, data andacknowledgments are exchanged in the same way as for the registrationstream.

Table 9 summarizes the content of an example Random Access Messageburst. The burst structure is the same as an uplink data burst on atraffic channel TCH. For an uplink data burst, the information symbolscarry data or in-and signaling or both.

TABLE 9 Duration Contents  10 μsec ramp-up 146 μsec training symbols a₁,a₂, . . ., a₇₃ 364 μsec information symbols h₁, h₂, . . ., h₁₈₂  10 μsecramp-down  15 μsec inter-burst guard time

The RA burst information symbols, in one embodiment, have the fields asshown in Table 10.

TABLE 10 Random Access Message Field # of Bits RAType 3 ID 15 UTTxPwr 5Total 23

The meanings of the symbol sets are as follows:

-   -   RAType: the type of the RA burst as described in association        with Table 8.    -   ID: the registration identifier, either the RID or, for page        responses, the PID. This field can be used by the base station        to prioritize stream requests. User terminals with a higher        priority can be identified by the RID or PID and be granted a        stream in preference to other users. The ID is also used to        access the registration account and information of the        requesting user terminal.    -   UTTxPwr: the power used by the user terminal to transmit the        burst. Anyone or more of these fields may be deleted or modified        and more fields may be added to particular applications.

The RAType field allows for there to be different types of RA messagessent on the channel. Table 11 lists possible examples that can besupported with a three bit field. Further or different types of RAmessages can be used depending upon the particular nature of thenetwork. More bits can be used to allow for still more different typesof messages. As an alternative, the user terminal may send a differentRA burst depending on the circumstances as listed in Table 11. All ofthe RA bursts in Table 8 are sent on the random access channel assignedto the user terminal by the base station. In one embodiment, the RAchannels are a set of channels that are also used for traffic.

TABLE 11 Value Symbol Meaning 000 RA-rts stream request 001 RA-pingkeep-alive poll request 010 RA-rts-short short stream request 011RA-rts-directed directed stream request 100 RA-page response streamrequest due to page 101 RA-rts-UM stream request, unacknowledged mode110 RA-rreq registration request

The meanings of the symbol sets are as follows:

-   -   RA-rts will be discussed further below and is the mechanism with        which the user terminal can open a new communications stream        following registration.    -   RA-ping: can be used to alert the base station to the location,        channel characteristics and activity of a user terminal without        opening a stream. Pinging the base station can be used to keep a        registration alive.    -   RA-rts short, -directed and -UM: can be used to open special        types of streams.    -   RA-page response: can be sent when the user terminal has no data        to transmit but is requesting that a stream be opened in        response to a page from the base station. In some systems, it        may be preferred that the base station open the stream directly        without first paging the user terminal as discussed above.    -   RA-rreg: can be used to open a new registration or change an        existing registration. As mentioned above, a user terminal uses        the RA bursts after registration, however, it may be useful in        network management for a single user terminal to have two        registrations for different individuals, different accounts,        different types of communications or other reasons.

Access Assignment Burst

The user terminal transmits any random access message such as RA-rts onthe uplink side of the random access channel. The base station uses thedownlink portion of the random access channel to grant random accessrequests and to assign resources to the requested data stream using anAA (Access Assignment) message. The AA message can have differentformats. One format is shown in Table 12.

TABLE 12 Access Assignment Message Field # of Bits ID 15 AAType 3modClassUp 5 modClassDown 5 frameDec 3 resource ibChan 6 pwrCtrl 4timingAdjust 5 tOffset spChan 3 Total 49

The meanings of the symbol sets are as follows:

-   -   ID: the id of the user terminal, either the RID or PID that was        transmitted in the RA-rts.    -   modClassUp: identifies the modulation and coding used for the        uplink.    -   modClassDown: identifies the modulation and coding used for the        downlink.    -   frameDec: defines fractional rate channels. resource ibChan:        indicates the uplink/downlink resource pair that is assigned to        the stream.    -   pwrCtrl: a power adjustment for the UT to apply to subsequent        transmissions.    -   timingAdjust: a timing adjustment for the UT to apply to        subsequent transmissions.    -   tOffset: training sequence offset adjustment for the UT to apply        to subsequent transmissions.    -   AAType: indicates the type of Access Assignment message. Many        different possible types are possible. Table 13 provides one        example set of AA types.

TABLE 13 Value Symbol Meaning 000 AA-cts stream grant 001 AA-rejectrequest rejected 010 AA-ping-ack keep-alive poll acknowledgment 011AA-cts-short short uplink grant 100 AA-cancel cancel previous false page101 AA-prev-short-ack previous short uplink was successful 110AA-invalid-ack received RA is not valid 111 AA-req-ack registrationgrant

The meanings of the symbol sets are as follows:

-   -   AA-cts: (Access Assignment-clear-to-send) begins a stream with        the sending user terminal based on the parameters in the AA-cts        message. An AA-cts can be sent in response to any of the RA        messages and is particularly appropriate for RA-rts, RA-ping,        RA-rts-directed, RA-page-response, and RA-rreg. This allows the        base station to open a stream even if the user terminal was not        aware of the need to open a stream. The next communication will        be data in the opened stream. As mentioned above, data will be        transferred until the corresponding stream data buffers are        emptied. Typically the stream is then closed. However, the        stream may be closed upon the occurrence of many other events as        well.    -   AA-reject: can be used to reject the request and direct the UT        to start a timer before sending an RA message. Such a response        can relieve congestion on a busy base station. The UT in        response may elect to wait or to send an RA-rts to another base        station that has better traffic availability.    -   AA-ping-ack: acknowledges the RA-ping and resets the timers for        the registration. The pinging process can be used to prevent a        registration from expiring for lack of traffic. Maintaining the        registration allows a stream to be opened immediately with e.g.        an RA-rts and an AA-cts. If the registration expires then the        registration process before a data stream can be opened.    -   AA-cts-short, and AA-prev-short-ack: can be used for special        types of streams.    -   AA-cancel: can be used to respond to an RA-page-response when no        page was sent or the paging condition no longer applies.    -   AA-invalid-id: can be used to notify the UT that it is using a        RID or PID that has expired or is not valid with the responding        base station. The UT can use the information in the AA to        request that a new registration stream be opened by sending e.g.        RA-rreq.    -   AA-reg-ack: is the acknowledgment of RA-rreq that begins a        registration stream.

As mentioned above, the base station can send a page to the UT directingthe UT to send an RA-page-response message to the base station. In oneembodiment, this reduces the control traffic overhead by using a pagingchannel. The paging channel can be efficiently utilized by the basestation and the page can allow random access channel assignments thatincrease the channel efficiency of establishing the desired data stream.The page bursts are transmitted on a paging channel which may be usedexclusively for pages or it may be shared with other functions such as abroadcast channel or a control channel. Alternatively a section of atraffic channel can be used for pages.

Pages will contain an indication of the base station sending the pageand of the user terminal being paged, typically the PID. If the UT isalready registered then the page does not need to also include anyinformation about how to respond to the page because this informationcan be included in the registration data exchange stream. In theembodiment discussed above, the UT will respond to a page in the randomaccess channel by sending a RA-page-response message, however othertypes of responses are also possible.

Traffic Channel Burst Structure

In one embodiment, a user terminal forms a relationship with a basestation called a registration or session. This registration begins bylistening to a BCH (Broadcast Channel) and ends with a handover,timeout, or disconnection. The first step of registration isaccomplished by a user terminal by sending a CR (Configuration Request)burst and receiving a CM (Configuration Message) burst. As describedabove, the CM contains basic configuration parameters such as hoppingsequence calculation parameters. Using the information from the CM, theuser terminal then opens an unauthenticated registration stream. Duringthe registration stream, identities and capabilities are exchanged,operating parameters are set, and a RID (Registration Identifier) andPID (Paging Identifier) are assigned. Later, streams may be created andattached to this RID, or PID, and operating parameters. The specificdetails of registration are not provided here. Many other registrationscenarios are also possible within the scope of the present invention.

The CM contains sufficient information for the user terminal to learnits distance and RF path-loss to the base station, correct its timingadvance, adjust its power control, and learn the parameters of frequencyhopping (e.g. frame numbering and BSCC. Based on this information fromthe CM, the user terminal, when it has data to transmit, can start asession, beginning with a RA-rreq (Random Access—registration request).If resources are available, the base station sends an AA-reg-ack (AccessAssignment—registration-acknowledgment) to the user terminal assigning atraffic channel for the registration process. The base station and userterminal exchange various access control parameters including encryptionkeys on this established stream. Finally a RID and PID are assigned.Using a RID or PID, the user terminal can establish secure streams inwhich it transmits and receives data packets on a TCH.

In spatial diversity radio communications systems, the present inventionallows communications on the traffic channel (TCH) to start withreasonably accurate timing, frequency, and spatial diversity parameters.Beginning with more accurate parameters avoids the added latency ofusing several frames to gradually determine channel information. In oneembodiment, the user terminals transmit omni-directionally from a singleantenna and the base station uses spatial diversity antennas to receiveand transmit using spatial diversity parameters. This allows signalstransmitted on the same channel from e.g. different locations to beresolved and it allows the base station to send different signals todifferent user terminals on a single frequency. The registration processincludes enough signaling for the base station to develop an accurateset of timing, frequency, and spatial parameters for sending any pages.However, in one embodiment, pages are sent in all directions, in casethe user terminal has moved after registration or radio channelconditions have changed. In addition, as described above, the uplinkrandom access bursts also have a fairly long training sequence. Thisallows the base station to refine the prior spatial processingparameters in the event that the user terminal has moved or the channelhas changed.

A traffic channel (TCH) burst is transmitted by a user terminal or abase station in order to send traffic over the traffic channel. In oneembodiment, TCH bursts are transmitted with idle bits when there is nodata to transmit in order to maintain timing and spatial parameters. Itis transmitted after CR and CM have been exchanged, after registrationand after a stream has been opened on an assigned channel for datatraffic. Accordingly, timing and frequency offset, as well as spatialsignatures are already reasonably well-established. In one embodiment,timing is known to less than plus or minus two symbol times.

The TCH burst is composed of several fields which are listed in Table14. The durations are described in terms of microseconds. In oneembodiment, a symbol period is 2 microseconds and the uplink anddownlink bursts differ as shown. Alternatively, the bursts may bestructured so that the uplink and downlink bursts have the samestructure. The network may also be a network of peers so that uplink anddownlink cannot be defined.

TABLE 14 Traffic Channel (TCH) Burst fields Duration Duration UplinkDownlink Contents  10 μsec  10 μsec ramp - up 146 μsec  68 μsec trainingsymbols (73, 34) 364 μsec 988 μsec information symbols (182, 494)  10μsec  10 μsec ramp - down  15 μsec  14 μsec inter-burst guard time

The training symbols are allocated 146 or 68 microseconds whichcorresponds to 73 or 34 symbols in order to allow the signal to be moreaccurately received and demodulated in the event that there has been anydrift or movement between terminals. The training symbols are discussedin more detail below.

The 364 or 494 information symbols are constructed from the transmitdata buffers. In the present embodiment, the TCH burst can be modulatedin a variety of ways in order to increase data capacity of the system.

Training Sequences

For the TCH burst, timing and frequency offset are already reasonablywell known due to the earlier exchange of CR and CM and registration. Asa result, the training sequences can be simpler. For the uplink burst,the training sequence symbols are selected by the user terminal based onthe BSCC and a value assigned to the user terminal by the base station.This allows bursts from different user terminals to be identified anddistinguished from one another. The core sequence can alternatively beselected based on a serial number, product number, ID number or otherstored number of the user terminal. In one embodiment, the trainingsequence has three parts, a 5 symbol prefix, a 63 symbol core and a 5symbol suffix. The prefix is made up of the last 5 symbols of the coreand the suffix is made up of the first 5 symbols of the core. Thedownlink training sequence is constructed similarly but has only a 24symbol core for a total of 34 symbols. The particular length and symbolset for the training sequence is not important to the present invention,provided that the sequence is known. Many different configurations forthe training sequence are possible. Similarly, it is not necessary todistinguish uplink and downlink sequences. However, for simplicity, thepresent invention shall be illustrated using the example of the 73symbol uplink training sequence discussed above.

In use, the particular sequences are typically generated using a look-uptable. The values in the table are selected based on autocorrelation,cross correlation, periodicity and similar properties. The bounds onauto and cross correlations help to make delayed versions of thesesequences to appear partially uncorrelated to a least squares beamformerwhich resolves them.

Standard Uplink and Downlink Burst

As can be seen from the description above, several different bursts havethe same structure. So, for example, in the uplink, the RA burst (Table9) and the TCH burst (Table 14) have the same structure. Even the CRburst (Table 5) has a training sequence that starts at the same symbolposition. For the downlink, the CM burst (Table 7), AA burst, and TCHburst (Table 14) all have the same structure. As a result, any of thelisted downlink bursts can be sent in any downlink slot of the framedescribed above. Bursts of a particular type can be directed to aparticular group of time slot and frequency resources or the bursts canbe mixed. For example, a particular frame or some other grouping of timeslot and frequency resources can be designated as a control channel andcarry only CR, CM, RA and AA bursts. Another set of resources can bedesignated as a traffic channel and carry only TCH bursts.Alternatively, as described above, the slots of a broadcast channelframe can be used for broadcast, control, random access and trafficchannels. In addition, the slots of any frame can be used to carrymessages of the broadcast, control, random access and traffic channels.

The bursts described herein are intended as examples only and more orfewer types of bursts can be used. The bursts can be classified in avariety of different ways and grouped into logical channels. As oneexample, the system can be characterized as having a broadcast channelBCH, control channel CCH and a traffic channel TCH. In this system theBCH has only BCH bursts and the TCH has only TCH bursts. The CCHincludes the CR, CM, RA, AA, and Page (PCH) bursts. The system can alsobe characterized as having a broadcast channel BCH, configurationchannel CCH, random access channel RACH, and traffic channel TCH.According to this taxonomy, the CR and CM belong to the CCH while theRA, AA and PCH belong to the RACH. The present invention does not dependon how bursts are characterized and can be applied to a wide range ofdifferent communications systems.

The common structure of the bursts allows any burst to be sent in anyslot. Except for the broadcast channel, all of the bursts have atraining sequence in the same symbol position and almost all of thebursts have the exactly the same structure. As a result, the bursts canall be demodulated in exactly the same way. Once the information symbolsare demodulated they can be passed to higher layers for appropriate use.This consistency in the burst structures provides for more flexibilityin the resource allocation of the system.

In one embodiment, the burst structures can be characterized as astandard uplink burst and a standard downlink burst. The standard uplinkburst can be used for RA and TCH bursts, carrying the same informationas discussed above. The standard downlink bursts can be used for CM, AAand TCH, carrying the information as discussed above. Pages can also betransmitted in the standard downlink burst. The bursts can be structuredas described above, or alternatively as shown in Table 15. This burststructure is depicted also in the diagrams of FIGS. 1 and 2. Thestandard bursts of Table 15 have less training than the burst describedabove, but also include a FACCH (fast associated control channel) whichcan be used to transmit control and overhead data of any kind. In somesystems, the FACCH can be used for messages regarding handovers. Inother systems, the FACCH can be used for messages regarding modulationclass or channel quality changes. As with the structures above, eachsymbol takes 2 μsec. Also as with the structures above, variations andmodifications can be made to suit specific implementations.

TABLE 15 Standard Burst (SUL, SDL) fields Duration Duration UplinkDownlink Contents  10 μsec  10 μsec ramp - up 114 μsec  68 μsec trainingsymbols (73, 34)  32 μsec FACCH (16) 364 μsec 920 μsec informationsymbols (182, 460)  32 μsec FACCH (16)  36 μsec training symbols (18) 10 μsec  10 μsec ramp - down  15 μsec  14 μsec inter-burst guard time

FIG. 1 shows an uplink burst of 545 μsec, the components of which are ashort 10 μsec ramp up 101, and a 68 μsec training sequence 102. Thetraining sequence can be selected in many different ways as describedabove. For example, it can be selected from a list of orthogonaltraining sequences based on the nature of the burst, an identificationof the transmitting terminal or the receiving terminal or an assignmentfrom the transmitting or receiving terminal. In one embodiment, thetraining sequences are grouped based on the tOffset value describedabove. For control channel messages (CR, CM, RA, AA) one or two tOffsetvalues are permitted and the rest of the tOffset values are used fortraffic channel (TCH) bursts. The selected training sequence is thenmodified or constructed by taking the selected sequence and applying afunction of the base station or user terminal ID.

These sections are followed by 364 μsec of information symbols 103 and a32 μsec FACCH 104. The information symbols will depend on the nature ofthe burst and can be registration, request, control or user data amongothers. The burst closes with a 10 μsec ramp-down 105 and a 15 μsecinterburst guard time 106. In the frame structures of the presentinvention, the interburst guard time will be followed either by anotherramp-up for the next burst, a transition guard time preceding downlinkbursts or an interframe guard time.

Similarly, FIG. 2 shows a standard downlink burst of 1090 μsec, thecomponents of which are a short 10 μsec ramp up 201, a 68 μsec trainingsequence 202, and a 32 μsec FACCH 203. The training sequence can beselected in any of the different ways as described above or others.These sections are followed by 920 μsec of information symbols 204. Theinformation symbols will depend on the nature of the burst and can beregistration, assignment, control or user data among others. The burstcloses with a 36 μsec tail training sequence 205, a 10 μsec ramp-down206 and a 14 μsec interburst guard time 207. In the frame structures ofthe present invention, the interburst guard time will be followed eitherby another ramp-up for the next burst, a transition guard time precedingdownlink bursts or an interframe guard time.

The tail training sequence aids in maintaining timing and frequencyduring the longer information symbol set. The training sequences ateither end provide two advantages. First, the greater distance betweenthe training sequences allows for a more accurate determination of thefrequency or phase offset during any burst. Second, by placing thetraining sequences at opposite ends of and outside of the informationsymbols, the accurate frequency offset from the training sequences canbe applied to the information symbols by interpolation. In some systems,all the training or additional training is placed in the middle of theinformation symbols. This requires an extrapolation in order todetermine the timing at the end of the information symbols.Extrapolation is inherently less accurate than interpolation. The tailtraining sequence may be the same as or different from the firsttraining sequence. If the first training sequence is a repetition ofsome core sequence, then the tail training sequence can be identical butwith fewer repetitions. Alternatively, the tail training sequence can bea truncated variation of the first training sequence.

Traffic Channel Frame Structure

As described above, the frame structure can support broadcast, control,random access and traffic channel bursts. All of the bursts describedabove can be used in the frame. An example of such a frame is shown, forexample in Table 4 above. This frame is described in further detail withrespect to Table 16 and FIG. 3.

TABLE 16 Standard Frame fields Duration Duration Duration UplinkDownlink System Contents 545 μsec slot #1 545 μsec slot #2 545 μsec slot#3 10 μsec transition guard time 1090 μsec slot #1 1090 μsec slot #21090 μsec slot #3 85 μsec inter-frame guard time

The example frame of FIG. 3 has three adjacent 545 μsec uplink slots301, 302, 303, in a single time sequence. The uplink slots are followedby a sequence of three adjacent 1090 μsec downlink slots 305, 306, 307.In FIG. 3, there is no gap between each uplink slot nor between eachdownlink slot, however, as shown in FIGS. 1 and 2, each slot includes aninterburst guard time. This interburst guard time can instead becharacterized as belonging to the frame and not to the slot, in whichcase there is a gap between each slot. In addition, between the uplinkslots and the downlink slots an additional 10 μsec uplink to downlinktransition time is provided. This time can be used by terminals toswitch between receive and transmit modes or transmit and receive modes.

An 85 μsec interframe guard time is provided after the downlink slots.The length of this as well as any of the other guard times can bemodified to suit any particular implementation of the present invention.The interframe guard time helps a receiving remote user terminal. Afterthe bursts of downlink slot #3 are transmitted, there will be apropagation time delay before the bursts have traveled past aparticularly distant remote receiver that is communicating with the basestation. Following the third downlink slot, uplink bursts will betransmitted. These can be transmitted with a timing advance so that theyare received by the base station within the appropriate uplink slot ofthe frame. For the most remote user terminals a significant timingadvance may be applied. These remote slot #1 uplink bursts can interferewith the base station's slot #3 downlink bursts unless a sufficientguard time is provided. 85 μsec provides a range of up to 15 km betweenthe base station and the most remote user terminals. 85 μsec isconsidered appropriate for the present example but may be increased ordecreased based on expected base station ranges as well as otherfactors.

While the example of Table 16 shows that the uplink slots always precededownlink slots, the ordering may be reversed. As can be seen from Table3, in a repeating frame, if the downlink slots are before the uplinkslots in a frame, then those downlink slots will still follow the uplinkslots of the previous frame. In addition, the frame is shown as havingthe uplink and downlink slots, respectively, adjacent to each other.Alternatively, the uplink and downlink slots can alternate or be groupedin some other way. The ordering of uplink and downlink slots describedabove simplifies the operation of the network and reduces demands onbase station and user terminal performance. It also requires less guardtime than many other frame structures. Finally, the uplink and downlinkslots are shown as being equal in number. This configuration works wellfor two-way communications in a traffic channel but can be modified tosuit particular system demands. For example, as shown in Table 3,broadcast channel bursts may be added to the frame in any selectedlocation. For some systems, it may be preferred to designate anadditional uplink or downlink slot for system information, datatransmitted to many users or to more completely compensate for asymmetryin data traffic demands.

FIG. 3 further shows that the downlink slots are twice as long as theuplink slots and, accordingly, twice as many symbols can be transmitted.Specifically, as shown in FIGS. 1 and 2 and Table 15, an uplink burstcarries 182 information symbols, while a downlink burst carries 460information symbols or about 2.5 times more symbols. In the trafficburst of Table 14, the uplink carries 182 information symbols and thedownlink 494 or about 2.7 times more information symbols in thedownlink. The actual data rate of the uplink and downlink bursts aredetermined in part by the number of information symbols transmitted andalso, in part, by the modulation class used for the uplink and downlinktransmissions.

Modulation Classes

As described above, some of the messages communicated between the basestation and the user terminal including utClass, modClassUp, andmodClassDown can be used to set or change the modulation class used fortransmitting uplink and downlink bursts. Alternatively, the FACCH oranother message can be used to set or adjust the modulation class used.The modulation classes provide different types of modulation and codingwhich together vary the number of bits per symbol. The modulationclasses can be selected based on terminal capabilities, channel qualityor a variety other factors. They can be changed in any number ofdifferent ways. The particular number and type of modulation classes cantake many different forms as appropriate to accommodate networkcapacities, channel quality and cost targets.

In one embodiment, there are 9 different modulation classes as shown inTable 17. The different modulation classes differ in modulation schemeas well as in encoding. The encoding can include error detection andcorrection, puncturing, block coding and block shaping. Other types ofmodulation and encoding can be used depending on the needs of aparticular application. The bit per symbol rates are approximate inTable 17 but provide an indication of a range of data rates that can beaccomplished using the same number of symbols. Using the values in Table15 of 182 uplink and 460 downlink information symbols per burst, amodulation class 0 burst would carry 91 or 230 bits, respectively. Amodulation class 8 burst on the other hand carries 728 and 1840 bits,respectively.

TABLE 17 Modulation Classes Bits/Uplink Bits/Downlink Signal ModClassBits/Sym Burst Burst Set 0 .5 91 230 BPSK 1 .67 121 308 BPSK 2 1 182 460QPSK 3 1.5 273 690 QPSK 4 2 364 920 8-PSK 5 2.5 455 1150 8-PSK 6 3 5461380 12-QAM 7 3.5 637 1610 16-QAM 8 4 728 1840 24-QAM

The modulation classes can also be adjusted to achieve a particular datarate ratio between uplink and downlink as well as to accommodate thegreater capabilities of a base station as compared to a remote terminal.The ratio of downlink symbols per uplink symbol is approximately 2.5:1.This is believed to be a practical data rate ratio for many Internetapplications. If the base station and the user terminal use the samemodulation class, then the data rate ratio will also be about 2.5:1.However, by using different modulation classes, the data rate ratio canbe varied between about 0.32:1 (UT at modclass 8, BS at modclass 0) toabout 20:1 (UT at modclass 0, BS at modclass 8). In some applications,the BS will frequently transmit user data using a modulation class thatis one step higher than the modulation class of the user terminal. Thisprovides a data rate ratio of from 2.9:1 to 3.8:1. As can be seen, themodulation classes provide a great amount of flexibility in setting theoperating parameters of the system.

The lower modulation classes require less energy to transmit and causeless interference with other users at the same base station.Accordingly, the system can be configured to prefer lower modulationclasses. On the other hand, the higher modulation classes transmit athigher data rates so that data buffers will be emptied sooner. For manytypes of data transfer, the higher data rate will mean shorter sessionsso that more users can be accommodated. If a user is sending andreceiving e-mail, for example, a higher data rate will transfer thee-mail faster, so that the session can be closed and the systemresources made available to another user. The selection of modulationclasses may depend not only on the amount of data to be transferred butthe relative amount in each direction. If the data to be transferred inone direction is much less than the data to be transferred in the otherdirection, then the direction with the lesser amount of data can beoperated at a much lower modulation class. Since the session will remainopen until the larger data buffer is empty, this will not delay closingthe session.

Base Station Structure

In one embodiment as discussed above, the present invention isimplemented in an SDMA (Spatial Division Multiple Access) radio datacommunications system. In such a spatial division system, each terminalis associated with a set of spatial parameters that relate to the radiocommunications channel between, for example, the base station and a userterminal. The spatial parameters comprise a spatial signature for eachterminal. Using the spatial signature and arrayed antennas, the RFenergy from the base station can be more precisely directed at a singleuser terminal, reducing interference with and lowering the noisethreshold for other user terminals. Conversely, data received fromseveral different user terminals at the same time can be resolved atlower receive energy levels. With spatial division antennas at the userterminals, the RF energy required for communications can be even less.The benefits are even greater for subscribers that are spatiallyseparated from one another. The spatial signatures can include suchthings as the spatial location of the transmitters, thedirections-of-arrival (DOAs), times-of-arrival (TOAs) and the distancefrom the base station.

Estimates of parameters such as signal power levels, DOAs, and TOAs canbe determined using known training sequences placed in digital datastreams for the purpose of channel equalization in conjunction withsensor (antenna) array information. This information is then used tocalculate appropriate weights for spatial demultiplexers, multiplexers,and combiners. Techniques well known in the art, can be used to exploitthe properties of the training sequences in determining spatialparameters. Further details regarding the use of spatial division andSDMA systems are described, for example, in U.S. Pat. Nos. 5,828,658,issued Oct. 27, 1998 to Ottersten et al. and 5,642,353, issued Jun. 24,1997 to Roy, III et al.

(SDMA) technology can be combined with other multiple access systems,such as time division multiple access (TDMA), frequency divisionmultiple access (FDMA) and code division multiple access (CDMA).Multiple access can be combined with frequency division duplexing (FDD)or time division duplexing (TDD).

FIG. 4 shows an example of a base station of a wireless communicationssystem or network suitable for implementing the present invention. Thebase station uses SDMA technology which can be combined with othermultiple access systems, such as time division multiple access (TDMA),frequency division multiple access (FDMA) and code division multipleaccess (CDMA). Multiple access can be combined with frequency divisionduplexing (FDD) or time division duplexing (TDD). The system or networkincludes a number of subscriber stations, also referred to as remoteterminals or user terminals, such as that shown in FIG. 5. The basestation may be connected to a wide area network (WAN) through its hostDSP 31 for providing any required data services and connections externalto the immediate wireless system.

To support spatial diversity, a plurality of antennas 3 is used to forman antenna array 4, for example four antennas, although other numbers ofantennas may be selected. Each antenna is an element of a four-elementarray 4. The antenna elements may have a spacing of from one-quarter tofour wavelengths of a typical carrier. In many applications, the spacingbetween antenna elements of each array can be less than two wavelengthsof the received signal. In general, the spacing between elements in anarray is selected to minimize grating lobes when transmissions from eachelement are coherently combined. As mentioned above, it is also possiblefor each array to have only a single element.

A set of spatial multiplexing weights for each subscriber station areapplied to the respective modulated signals to produce spatiallymultiplexed signals to be transmitted by the bank of four antennas. Thehost DSP 31 produces and maintains spatial signatures for eachsubscriber station for each conventional channel and calculates spatialmultiplexing and demultiplexing weights using received signalmeasurements. In this manner, the signals from the current activesubscriber stations, some of which may be active on the sameconventional channel, are separated and interference and noisesuppressed. When communicating from the base station to the subscriberstations, an optimized multi-lobe antenna radiation pattern tailored tothe current active subscriber station connections and interferencesituation is created. The channels used may be partitioned in anymanner. In one embodiment the channels used may be partitioned asdefined in the GSM (Global System for Mobile Communications) airinterface, or any other time division air interface protocol, such asDigital Cellular, PCS (Personal Communication System), PHS (PersonalHandyphone System) or WLL (Wireless Local Loop). Alternatively,continuous analog or CDMA channels can be used.

The outputs of the antennas are connected to a duplexer switch 7, whichin a TDD embodiment, may be a time switch. Two possible implementationsof the duplexer switch are as a frequency duplexer in a frequencydivision duplex (FDD) system, and as a time switch in a time divisionduplex (TDD) system. When receiving, the antenna outputs are connectedvia the duplexer switch to a receiver 5, and are converted down inanalog by RF receiver (“RX”) modules 5 from the carrier frequency to anFM intermediate frequency (“IF”). This signal then is digitized(sampled) by analog to digital converters (“ADCs”) 9. Finaldown-converting to baseband is carried out digitally. Digital filterscan be used to implement the down-converting and the digital filtering,the latter using finite impulse response (FIR) filtering techniques.This is shown as block 13. The invention can be adapted to suit a widevariety of RF and IF carrier frequencies and bands.

There are, in the example of GSM, eight down-converted outputs from eachantenna's digital filter 13, one per receive timeslot. The particularnumber of timeslots can be varied to suit network needs. While GSM useseight uplink and eight downlink timeslots for each TDMA frame, desirableresults can also be achieved with any number of TDMA timeslots for theuplink and downlink in each frame. For each of the eight receivetimeslots, the four down-converted outputs from the four antennas arefed to a digital signal processor (DSP) 31 an ASIC (Application SpecificIntegrated Circuit) or FPGA (Field Programmable Gate Array) (hereinafter“timeslot processor”) for further processing, including calibration,according to one aspect of this invention. For TDMA signals, eightMotorola DSP56300 Family DSPs can be used as timeslot processors, oneper receive timeslot. The timeslot processors 17 monitor the receivedsignal power and estimate the frequency offset and time alignment. Theyalso determine smart antenna weights for each antenna element. These areused in the SDMA scheme to determine a signal from a particular remoteuser and to demodulate the determined signal. In a WCDMA system, thechannels may be separated using codes in an FPGA and then furtherprocessed separately perhaps using separate DSPs for different users.Instead of being timeslot processors the processors are channelprocessors.

The output of the timeslot processors 17 is demodulated burst data foreach of the eight receive timeslots. This data is sent to the host DSPprocessor 31 whose main function is to control all elements of thesystem and interface with the higher level processing, which is theprocessing which deals with what signals are required for communicationsin all the different control and service communication channels definedin the system's communication protocol. The host DSP 31 can be aMotorola DSP56300 Family DSP. In addition, timeslot processors send thedetermined receive weights for each user terminal to the host DSP 31.The host DSP 31 maintains state and timing information, receives uplinkburst data from the timeslot processors 17, and programs the timeslotprocessors 17. In addition it decrypts, descrambles, checks errorcorrecting code, and deconstructs bursts of the uplink signals, thenformats the uplink signals to be sent for higher level processing inother parts of the base station.

Furthermore DSP 31 may include a memory element to store data,instructions, or hopping functions or sequences. Alternatively, the basestation may have a separate memory element or have access to anauxiliary memory element. With respect to the other parts of the basestation it formats service data and traffic data for further higherprocessing in the base station, receives downlink messages and trafficdata from the other parts of the base station, processes the downlinkbursts and formats and sends the downlink bursts to a transmitcontroller/modulator, shown as 37. The host DSP also manages programmingof other components of the base station including the transmitcontroller/modulator 37 and the RF timing controller shown as 33. The RFcontroller 33 reads and transmits power monitoring and control values,controls the duplexer 7 and receives timing parameters and othersettings for each burst from the host DSP 31.

The transmit controller/modulator 37, receives transmit data from thehost DSP 31. The transmit controller uses this data to produce analog IFoutputs which are sent to the RF transmitter (TX) modules 39.Specifically, the received data bits are converted into a complexmodulated signal, up-converted to an IF frequency, sampled, multipliedby transmit weights obtained from host DSP 31, and converted via digitalto analog converters (“DACs”) which are part of transmitcontroller/modulator 37 to analog transmit waveforms. The analogwaveforms are sent to the transmit modules 39. The transmit modules 39up-convert the signals to the transmission frequency and amplify thesignals. The amplified transmission signal outputs are sent to antennas3 via the duplexer/time switch 7. In a CDMA system, the signals may alsobe spread and scrambled using appropriate codes.

User Terminal Structure

FIG. 5 depicts an example component arrangement in a remote terminalthat provides data or voice communication. The remote terminal's antenna45 is connected to a duplexer 46 to permit the antenna 45 to be used forboth transmission and reception. The antenna can be omni-directional ordirectional. For optimal performance, the antenna can be made up ofmultiple elements and employ spatial processing as discussed above forthe base station. In an alternate embodiment, separate receive andtransmit antennas are used eliminating the need for the duplexer 46. Inanother alternate embodiment, where time division duplexing is used, atransmit/receive (TR) switch can be used instead of a duplexer as iswell known in the art. The duplexer output 47 serves as input to areceiver 48. The receiver 48 produces a down-converted signal 49, whichis the input to a demodulator 51. A demodulated received sound or voicesignal 67 is input to a speaker 66.

The remote terminal has a corresponding transmit chain in which data orvoice to be transmitted is modulated in a modulator 57. The modulatedsignal to be transmitted 59, output by the modulator 57, is up-convertedand amplified by a transmitter 60, producing a transmitter output signal61. The transmitter output 61 is then input to the duplexer 46 fortransmission by the antenna 45.

The demodulated received data 52 is supplied to a remote terminalcentral processing unit 68 (CPU) as is received data before demodulation50. The remote terminal CPU 68 can be implemented with a standard DSP(digital signal processor) device such as a Motorola series 56300 FamilyDSP. This DSP can also perform the functions of the demodulator 51 andthe modulator 57. The remote terminal CPU 68 controls the receiverthrough line 63, the transmitter through line 62, the demodulatorthrough line 52 and the modulator through line 58. It also communicateswith a keyboard 53 through line 54 and a display 56 through line 55. Amicrophone 64 and speaker 66 are connected through the modulator 57 andthe demodulator 51 through lines 65 and 67, respectively for a voicecommunications remote terminal. In another embodiment, the microphoneand speaker are also in direct communication with the CPU to providevoice or data communications. Furthermore remote terminal CPU 68 mayalso include a memory element to store data, instructions, and hoppingfunctions or sequences. Alternatively, the remote terminal may have aseparate memory element or have access to an auxiliary memory element.

In one embodiment, the speaker 66, and the microphone 64 are replaced oraugmented by digital interfaces well-known in the art that allow data tobe transmitted to and from an external data processing device (forexample, a computer). In one embodiment, the remote terminal's CPU iscoupled to a standard digital interface such as a PCMCIA interface to anexternal computer and the display, keyboard, microphone and speaker area part of the external computer. The remote terminal's CPU 68communicates with these components through the digital interface and theexternal computer's controller. For data only communications, themicrophone and speaker can be deleted. For voice only communications,the keyboard and display can be deleted.

General Matters

In the description above, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. It will be apparent, however, toone skilled in the art that the present invention may be practicedwithout some of these specific details. In other instances, well-knowncircuits, structures, devices, and techniques have been shown in blockdiagram form or without detail in order not to obscure the understandingof this description.

The present invention includes various steps. The steps of the presentinvention may be performed by hardware components, such as those shownin FIGS. 4 and 5, or may be embodied in machine-executable instructions,which may be used to cause a general-purpose or special-purposeprocessor or logic circuits programmed with the instructions to performthe steps. Alternatively, the steps may be performed by a combination ofhardware and software. The steps have been described as being performedby either the base station or the user terminal. However, many of thesteps described as being performed by the base station may be performedby the user terminal and vice versa. Furthermore, the invention isequally applicable to systems in which terminals communicate with eachother without either one being designated as a base station, a userterminal, a remote terminal or a subscriber station. Thus, the presentinvention is equally applicable and useful in a peer-to-peer wirelessnetwork of communications devices using spatial processing. Thesedevices may be cellular phones, PDA's, laptop computers, or any otherwireless devices. Generally, since both the base stations and theterminals use radio waves, these communications devices of wirelesscommunications networks may be generally referred to as radios.

In portions of the description above, only the base station is describedas performing spatial processing using adaptive antenna arrays. However,the user terminals can also contain antenna arrays, and can also performspatial processing both on receiving and transmitting (uplink anddownlink) within the scope of the present invention.

Furthermore, in portions of the description above, certain functionsperformed by a base station could be coordinated across the network, tobe performed cooperatively with a number of base stations. For example,each base station antenna array could be a part of a different basestation. The base station's could share processing and transceivingfunctions. Alternatively, a central base station controller couldperform many of the functions described above and use the antenna arraysof one or more base stations to transmit and receive signals.

The present invention may be provided as a computer program product,which may include a machine-readable medium having stored thereoninstructions, which may be used to program a computer (or otherelectronic devices) to perform a process according to the presentinvention. The machine-readable medium may include, but is not limitedto, floppy diskettes, optical disks, CD-ROMs, and magneto-optical disks,ROMs, RAMs, EPROMs, EEPROMs, magnet or optical cards, flash memory, orother type of media/machine-readable medium suitable for storingelectronic instructions. Moreover, the present invention may also bedownloaded as a computer program product, wherein the program may betransferred from a remote computer to a requesting computer by way ofdata signals embodied in a carrier wave or other propagation medium viaa communication link (e.g., a modem or network connection).

Many of the methods are described in their most basic form, but stepscan be added to or deleted from any of the methods and information canbe added or subtracted from any of the described messages withoutdeparting from the basic scope of the present invention. It will beapparent to those skilled in the art that many further modifications andadaptations can be made. The particular embodiments are not provided tolimit the invention but to illustrate it. The scope of the presentinvention is not to be determined by the specific examples providedabove but only by the claims below.

It should also be appreciated that reference throughout thisspecification to “one embodiment” or “an embodiment” means that aparticular feature may be included in the practice of the invention.Similarly, it should be appreciated that in the foregoing description ofexemplary embodiments of the invention, various features of theinvention are sometimes grouped together in a single embodiment, figure,or description thereof for the purpose of streamlining the disclosureand aiding in the understanding of one or more of the various inventiveaspects. This method of disclosure, however, is not to be interpreted asreflecting an intention that the claimed invention requires morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive aspects lie in less than allfeatures of a single foregoing disclosed embodiment. Thus, the claimsfollowing the Detailed Description are hereby expressly incorporatedinto this Detailed Description, with each claim standing on its own as aseparate embodiment of this invention.

1. A radio of a radio communications system having a transceiver forcommunicating with other radios of the radio communications system overradio channels using a repeating time division frame, the frame having aplurality of slots, at least one of the slots comprising: a firsttraining sequence for use in receiving an information sequence; aninformation sequence after the first training sequence carryinginformation from the radio; and a second training sequence after theinformation sequence for use in receiving the information sequence, thesecond training sequence also being a control sequence.
 2. The radio ofclaim 1, further comprising a control sequence before the informationsequence.
 3. The radio of claim 2, wherein the control sequenceindicates one of a plurality of different transmission modes for theinformation sequence.
 4. The radio of claim 3, wherein the transmissionmode includes at least one of a modulation format and an encodingformat.
 5. The radio of claim 3, wherein the plurality of differenttransmission modes correspond to different data rates.
 6. The radio ofclaim 1, wherein the control sequence is immediately after the firsttraining sequence.
 7. The radio of claim 1, wherein the control sequencecomprises a fast associated control channel sequence.
 8. The radio ofclaim 6, wherein the control sequence comprises a fast associatedcontrol channel sequence.
 9. The radio of claim 1, wherein theinformation sequence is continuous, and wherein the second trainingsequence is adjacent to and after the information sequence.
 10. Theradio of claim 1, wherein one of the first and the second trainingsequences indicates a type for the information sequence.
 11. The radioof claim 10, wherein the type for the information sequence is selectedfrom one of a random access channel message, and a traffic channelmessage.
 12. The radio of claim 11, wherein the training sequence isselected from among different sets of training sequences, each setcorresponding to a type for the information sequence.
 13. The radio ofclaim 12, wherein the training sequences of each set are orthogonal tothe other training sequences of the set.
 14. The radio of claim 10,wherein the type for the information sequence is selected from one of aconfiguration message, a channel assignment message, and a data trafficmessage.
 15. A method comprising: sending a first training sequencewithin a slot of a repeating time division frame, the first trainingsequence being for use in receiving an information sequence; sending aninformation sequence carrying information to a receiver within the slotafter the first training sequence; and sending a second trainingsequence within the slot after the information sequence for use inreceiving the information sequence, the second training sequence alsobeing a control sequence.
 16. The method of claim 15, further comprisingsending a control sequence before the information sequence.
 17. Themethod of claim 16, wherein the control sequence indicates one of aplurality of different transmission modes for the information sequence.18. The method of claim 17, wherein the plurality of differenttransmission modes correspond to different data rates.
 19. The method ofclaim 16, wherein the control sequence comprises a fast associatedcontrol channel sequence.
 20. The method of claim 15, wherein theinformation sequence is continuous, and wherein the second trainingsequence is adjacent to and after the information sequence.
 21. Themethod of claim 15, wherein one of the first and the second trainingsequences indicates a type for the information sequence.
 22. The methodof claim 21, wherein the type for the information sequence is selectedfrom one of a random access channel message, a configuration message, achannel assignment message, and a traffic channel message.
 23. Themethod of claim 21, wherein the training sequence is selected from amongdifferent sets of training sequences, each set corresponding to a typefor the information sequence.
 24. An apparatus comprising: a processorto construct a burst for transmission in a slot of a repeating timedivision frame, the burst having a first training sequence for use inreceiving an information sequence, the information sequence after thefirst training sequence carrying information from a transmitter of theapparatus and a second training sequence after the information sequencefor use in receiving the information sequence, the second trainingsequence also being a control sequence; and the transmitter for sendingthe burst constructed by the processor.
 25. The apparatus of claim 24,wherein the slot further has a control sequence before the informationsequence.
 26. The apparatus of claim 25, wherein the control sequenceindicates one of a plurality of different transmission modes for theinformation sequence.
 27. The apparatus of claim 24, wherein theinformation sequence is continuous, and wherein the second trainingsequence is adjacent to and after the information sequence.
 28. Theapparatus of claim 27, wherein the control sequence indicates one of aplurality of different transmission modes for the information sequence.29. The apparatus of claim 24, wherein one of the first and the secondtraining sequences indicates a type for the information sequence.
 30. Aradio of a radio communications system having a transceiver forcommunicating with other radios of the radio communications system overradio channels using a repeating time division frame, the frame having aplurality of slots, at least one of the slots comprising: a firsttraining sequence for use by the other radios in receiving aninformation sequence; an information sequence after the first trainingsequence carrying information from the radio; and a second trainingsequence for use in receiving the information sequence, wherein one ofthe first and the second training sequences indicates a type for theinformation sequence.
 31. The radio of claim 30, wherein the firsttraining sequence indicates the type.
 32. The radio of claim 30, whereinthe type for the information sequence is selected from one of a randomaccess channel message and a traffic channel message.
 33. The radio ofclaim 30, wherein the type for the information sequence is selected fromone of a configuration message, a channel assignment message, and a datatraffic message.
 34. The radio of claim 33, wherein the trainingsequence is selected from among different sets of training sequences,each set corresponding to a type for the information sequence.
 35. Theradio of claim 34, wherein the training sequences of each set areorthogonal to the other training sequences of the set.
 36. The radio ofclaim 30, wherein the second training sequence comprises a controlsequence.
 37. The radio of claim 36, wherein the control sequencecomprises a fast associated control channel sequence.
 38. The radio ofclaim 37, wherein the control sequence indicates one of a plurality ofdifferent transmission modes for the information sequence.
 39. The radioof claim 38, wherein the transmission mode includes at least one of amodulation format and an encoding format.
 40. A method comprising;sending a first training sequence in a slot of a repeating time divisionframe for use in receiving an information sequence; sending aninformation sequence in the slot after the first training sequencecarrying information to a receiver; and sending a second trainingsequence in the slot for use in receiving the information sequence,wherein one of the first and the second training sequences indicates atype for the information sequence.
 41. The method of claim 40, whereinthe first training sequence indicates the type.
 42. The method of claim40, wherein the type for the information sequence is selected from oneof a random access channel message, a configuration message, a channelassignment message, and a traffic channel message.
 43. The method ofclaim 40, wherein the training sequence is selected from among differentsets of training sequences, each set corresponding to a type for theinformation sequence.
 44. The method of claim 40, wherein the secondtraining sequence comprises a control sequence.
 45. The method of claim44, wherein the control sequence indicates one of a plurality ofdifferent transmission modes for the information sequence.
 46. Themethod of claim 45, wherein the transmission mode includes at least oneof a modulation format and an encoding format.
 47. An apparatuscomprising; means for sending a first training sequence in a slot of arepeating time division frame for use in receiving an informationsequence; means for sending an information sequence in the slot afterthe first training sequence, the information sequence carryinginformation from the means for sending the information sequence; andmeans for sending a second training sequence in the slot for use inreceiving the information sequence, wherein one of the first and thesecond training sequences indicates a type for the information sequence.48. The apparatus of claim 47, wherein the first training sequenceindicates the type.
 49. The apparatus of claim 47, wherein the type forthe information sequence is selected from one of a random access channelmessage, a configuration message, a channel assignment message, and atraffic channel message.
 50. The apparatus of claim 47, wherein thetraining sequence is selected from among different sets of trainingsequences, each set corresponding to a type for the informationsequence.
 51. The apparatus of claim 47, wherein the second trainingsequence comprises a control sequence.
 52. The apparatus of claim 51,wherein the control sequence indicates one of a plurality of differenttransmission modes for the information sequence.
 53. The apparatus ofclaim 52, wherein the transmission mode includes at least one of amodulation format and an encoding format.
 54. An apparatus comprising; atransmitter to send a first training sequence in a slot of a repeatingtime division frame for use in receiving an information sequence, aninformation sequence carrying information from the transmitter in theslot after the first training sequence, and a second training sequencein the slot for use in receiving the information sequence; and aprocessor to select a training sequence as one of the first and thesecond training sequences to indicate a type for the informationsequence.
 55. The apparatus of claim 54, wherein the first trainingsequence indicates the type.
 56. The apparatus of claim 54, wherein theprocessor selects a training sequence for the type of the informationsequence from one of a random access channel message, a configurationmessage, a channel assignment message, and a traffic channel message.57. The apparatus of claim 54, wherein the processor selects thetraining sequence from among different sets of training sequences, eachset corresponding to a type for the information sequence.
 58. Theapparatus of claim 54, wherein the second training sequence comprises acontrol sequence.
 59. The apparatus of claim 58, wherein the controlsequence indicates one of a plurality of different transmission modesfor the information sequence.
 60. The apparatus of claim 59, wherein thetransmission mode includes at least one of a modulation format and anencoding format.